Maintenance-free type lead acid

ABSTRACT

This invention concerns a maintenance-free type lead acid cell which is in a normally sealed condition. The cell is characterized by structurally free, non-self-supporting plates separated from one another with highly absorbent flexible separators containing electrolyte and constrained within a container such that mechanical integrity is imparted to obtain a unitary self-supporting structure. Means are provided for maximum recombination of evolved gases and for discharge of excessively high pressure gas. A centroid element allows for operation in any indiscriminate attitude.



1. A MAINTENANCE-FREE TYPE LEAD ACID CELL WHICH SUSTAINS SUBSTANTIALOVERCHARGE IN ANY INDISCRIMATE ATTITUDE OF THE CELL, SAID CELL OPERATINGIN A NORMALLY SEALED CONFIGURATION UTILIZING AN "OXYGEN" CYCLE,COMPRISING: NON-SELF-SUPPORTING LEAD BASED GRIDS HAVING A HIGH HYDDROGENOVERVOLTAGE, SAID GRIDS PASTED WITH ACTIVE MATERIAL TO FORM POROUSPOSITIVE AND NEGATIVE PLATES; AN ELECTROLYTE ABSORBING AND RETAININGSEPARATOR MATERIAL CHARACTERIZED BY HAVING A HIGH HEAT OF WETTING ANDINTIMATELY CONTACTING ADJACENT, OPPOSITE POLARITY PLATES AN ELECRROLYTEABSORBED AND RETAINED BY SAID SEPARATOR AND BY SAID PLATES TO THE DEGREETHT NO FREE UNABSORBED ELECTROLYTE IID PRESENT IN THE CELL, SAID PLATESAND THIN LAYER OF ELECTROLYTE ON SAID ACTIVE MATERIAL SUFFICIENT TOSUSTAIN ELECTROCHEMICAL REACTIONS AT THE PLATES AND PERMITTING OXYGENTRANSFER TO AND FROM THE ACTIVE MATERIAL THROUGH A VOID VOLUME FORMED INSUBSTANTIALLY ALL OF THE PORES OF SAID PLATES, SAID TIN LAYER OFELECTROLYTE UNIFORMLY DISTRIBUTED THROUGHOUT SAID PLATES AND SAID VOIDVOLUME FORMED BY VIRTUE OF THE PRESENCE OF ONLY THE THIN LAYER OF AELECTROLYTE ON THE ACTIVE MATERIAL, AND A CONTAINER TIGHTLY CONTRASTINGSAID PLATES, SEPARATOR AND ABSORBED ELECTROLYTE UNDER FIRM STACKINGPRESSURE TO FORM S SELF-SUPPORTING INTEGRAL CELL.
 2. A cell according toclaim 1 in which the lead utilized in the grids is of greater than about99.9 percent by weight purity and contains no material to increaserigidity with accompanying degrees of reduction of hydrogen or oxygenovervoltage.
 3. A cell according to claim 1 in which each of saidpositive and negative plates comprises a continuous, unitary, pliable,structurally free lead sheet, forming a grid for said plates.
 4. A cellaccording to claim 1 in which a gas venting means having a vent exit isinserted into the cell to a point such that the venting exit is disposedat substantially the centroid of the cell. is further a valving meansdisposed over said vent normally biased in a closed position to retaingenerated gas at a positive pressure within said cell.
 5. A cellaccording to claim 3 in which separator material is disposed betweeneach of said positive and negative plates prior to insertion within saidcontainer; said plates and separator material separating said platestightly and spirally wound into a spiral configuration.
 6. A cellaccording to claim 1 having additionally edge surfaces of activematerial on said plates to aid in the recombination of gas.
 7. A cellaccording to claim 1 in which there is disposed between the containerand the stacked plates, separator and electrolyte subassembly, anelectrically insulated liner material electrically separating saidplates, separator and electrolyte subassembly from said container.
 8. Acell according to claim 1 in which a hydrophobic paste is incorporatedwithin the negative plate to minimize the degree of wetting of the plateby the electrolyte.
 9. A cell according to claim 6 in which separatormaterial extends beyond the edge surface of the lead plates, saidextended portion of the separator treated to be rendered hydrophobicthereby minimizing the degree of wetting of said extended to to allowfor maximum portion to allow for maximum availability of generated gasesto recombine with the edge surfaces of the plates.
 10. Amaintenance-free type lead acid cell operating under superatmosphericinternal pressure and in a normally sealed configuration utilizing an''''oxygen'''' cycle comprising: lead based grids having a high hydrogenovervoltage and in which the lead utilized in the grids is of greaterthan about 99.9 percent by weight purity, said grids pasted with activematerial to form porous positive and negative plates; an electrolyteabsorbing and retaining separator material having a high heat ofwetting, high surface area and porosity of about 85 to 95 percent,intimately contacting adjacent opposite polarity plates; a liquidelectrolyte absorbed and retained by said separator and by said platesto the degree that no free unabsorbed electrolyte is present in thecell; said plates containing a thin layer of electrolyte on said activematerial sufficient to sustain electrochemical reactions at the platesand permitting oxygen transfer to and from the active material through avoid volume formed in substantially all of the pores of said plates,said thin layer of electrolyte uniformly distributed throughout saidplates and said void volume formed by virtue of the presence of only thethin layer of electrolyte on the active material; and a containerencapsulating and tightly constraining said plates, separator andabsorbed electrolyte under firm stacking pressure to form aself-supporting integral cell capable of use under any attitude.
 11. Acell according to claim 10 in which the electrolyte is present in arelatively starved amount.
 12. A maintenance-free type lead-acid celloperating in a normally sealed configuration utilizing an ''''oxygen<--> cycle including at least one porous positive plate, aT least oneporous negative plate, a liquid electrolyte in a starved amount, and aseparator material, in firm pressure contact with the plates, whichseparator absorbs and retains all the electrolyte except for thepresence of a thin layer of electrolyte distributed on the walls ofsubstantially all of the pores uniformly throughout the active materialof the cell plates, said pores which carry said thin film of electrolytebeing free of electrolyte except for said thin film, allowing the cellto be utilized in any position without leakage of electrolyte andpermitting the cell to sustain substantial overcharge rates by improvedavenues for oxygen transport and recombination within the cell.
 13. Acell according to claim 12 in which the separator is a non-woven, fiberglass matting having a high degree of wettability.
 14. A cell accordingto claim 13 in which the fibers of the fiber glass have a diameter inthe range of from about 0.2 to about 10 microns.
 15. A cell according toclaim 13 in which the fibers of the fiber glass have a surface areabetween about 0.1 to 20 square meters per gram of silica.
 16. A cellaccording to claim 12 in which the separator material has a porosity inthe range of 85 to 95 percent.
 17. A cell according to claim 12 in whichthe separator is a non-woven, fiber glass matting having a porositybetween about 85 and 95 percent and wherein the fiber diameter of thefibers of the fiber glass is in the range of about 0.2 to 10 microns andhas a surface area in the range of about 0.1 to 20 square meters pergram of silica.
 18. A cell according to claim 12 in which said positiveand negative plates comprise non-self-supporting lead based grids havinga high hydrogen overvoltage.
 19. A cell according to claim 18 whereinsaid plates, separator and absorbed electrolyte are constrained tightlyunder firm stacking pressure to form a self-supporting integral cell.20. A cell according to claim 18 in which the lead utilized in the gridsis of greater than about 99.9 percent by weight purity and contains nomaterials to increase rigidity with accompanying degrees of reduction ofhydrogen or oxygen overvoltage.
 21. In a maintenance-free normallysealed lead-acid electrochemical cell operative without significanthydrogen evolution comprising at least one porous pasted negative plate,at least one porous pasted positive plate, both plates utilizingnon-self supporting high purity lead grids, liquid acid electrolye,electrolyte absorbing and retaining separator, and a containerencapsulating the plates, separator and included electrolyte under firmstacking pressure, the improvement comprising the following features: a.electrolyte present in a starved amount so that there is no freeelectrolyte in the cell, substantially all of the electrolyte beingabsorbed within the interstices of the separator except for a smallamount of electrolyte present as a thin layer on the surface of asubstantial portion of the pores uniformly distributed throughout theplates producing an electrolyte-free void volume in said pores; and b.porous separator material having a high heat of wetting and high surfacearea and in intimate contact with the plates, said properties of theseparator together with the presence of only the starved amount ofelectrolyte and firm stacking pressure causing the separator to wickelectrolyte from the plates whereby the thin layer of electrolyte in theplates is obtained, said substantial portion of the pores having saidthin layer of electrolyte on the walls of the pores being sufficient inamount to enable improved oxygen access to the negative plate forrecombination therewith at significant rates of overcharge.
 22. Amaintenance-free type lead-acid cell operating under the oxygen cyclecapable of withstanding substantial rates of overcharge comprising: leadbased grids having a high hydrogen overvolTage and in which the leadutilized in the grids is of greater than about 99.9 percent by weightpurity, said grids pasted with active material to form porous positiveand negative plates; a porous electrolyte absorbing and retainingseparator composed of a matting of fiber glass in which the fibers havea diameter in the range of from about 0.2 to about 10 microns; acidliquid electrolyte absorbed and retained by said separator and by saidplates to the degree that no free unabsorbed electrolyte is present inthe cell, said plates containing a thin layer of electrolyte on saidactive materials permitting oxygen transfer to the negative materialfrom the positive active material through a void volume formed insubstantially all of the pores of said plates, said thin layer ofelectrolyte uniformly distributed throughout said plates and said voidvolume formed by virtue of the presence of only the thin layer ofelectrolyte on the active material; and a container encapsulating andtightly constraining said plates separator and absorbed electrolyteunder firm stacking pressure to form a self-supporting integral cellcapable of use under any attitude.
 23. A maintenance-free normallysealed lead-acid electrochemical cell operative without significanthydrogen evolution comprising at least one porous pasted negative plate,at least one porous pasted positive plate, both plates utlizingnon-self-supporting high purity grids, liquid acid electrolyte,electrolyte absorbing and retaining separator, and a containerencapsulating the plates, separator and included electrolyte under firmstacking pressure, in combination therewith the improvement comprising:a. electrolyte present in a starved amount so that there is no freeelectrolyte in the cell, substantially all of the electrolyte beingabsorbed within the pores of the separator except for a small amount ofelectrolyte present as a thin layer on the surface of the pores of theplate; and b. separator material having a high heat of wetting and highsurface area and in intimate contact with the plates.